1. Field of the Invention
The present invention relates generally to a friction modifying lubricant additive, and more particularly to lubricant additive including dispersed colloidal nanocarbon particles.
2. Description of the Related Art
A large reduction in friction coefficient and wear and improved extreme pressure failure load properties are demonstrated, which are particularly useful for lubricating oil compositions where the level of extreme pressure protection is needed in addition to low friction and wear.
Additives are used with lubricants in order to reduce friction and wear as well as to increase the load carrying capacity of the lubricants. The so called extreme pressure (EP) additives in lubricants are aimed for the lubricant's use under extreme pressure conditions, such as, for example, with the type of heavy equipment used for drilling, mining and other heavy industrial applications, for example, lubricants for open and enclosed gears, house roller and rails, and bearings. Organic compounds containing sulfur (S), phosphorus (P), chlorine (Cl), nitrogen (N), and boron (B), as well as organometallic compounds, especially, for example, zinc dialkyl dithiophosphates (ZDDP) and molybdenum dialkyldithiocarbamate (Mo-DTC) have been used widely as antiwear (AW) and/or EP additive components in lubricating oils.
Other additives that may be included in lubricants as anti-wear additives include fluorinated organic compounds, for example, polytetrafluorethylene (PTFE), which are thought to protect metal surfaces from wear by forming metal fluorides on the coated surfaces. One limitation of the highly fluorinated materials is their very low solubility in conventional lubricant base fluids such as natural and synthetic hydrocarbons and esters, which has effectively limited their application as solid additives Zinc dialkyl dithiophosphates with primary amines were shown to have better solubility in oils depending on the amine content. Partly-fluorinated compounds, particularly ZDDP, have better solubility in base oils and have been used as lubricant additives.
Fluorine-containing ZDDPs (F-ZDDPs) have also been used before in combination with certain molybdenum (Mo) additives, including soluble molybdenum additives, such as molybdenum dialkyl dithiophosphates, molybdenum dialkyl dithiocarbamates and molybdenum amide complexes. One limitation of F-ZDDP-Mo-containing additive combinations, however, is that the molybdenum additives frequently reduce the anti-wear effectiveness of the F-ZDDPs, which is highly undesirable.
Certain nanomaterials in powder and colloidal forms have been used as anti-friction and wear additives in a variety of base lubricants. Among them, detonation soot, which is a mixture of nanodiamond particles with different forms of sp2-bonded carbon, has been used in commercial Class I oils for more than two decades. For a long time, it was assumed that pure detonation nanodiamond (DND), which is purified to remove sp2 content as opposed to DND in the unpurified soot, was not suitable for lubrication, because of the abrasive nature of diamond particles. However, it was shown that, in combination with a dispersant, for example, 35 wt. % of magnesium (Mg) alcylobenzolesulphonate and 65 wt. % vegetable oil transesterificated with diethanolamine, and polytetrafluoroethylene (PTFE), the addition of DND results in decreased coefficient of friction in mineral oils of class I, as compared to a composition when only the dispersant and PTFE additives are used. (See Ivanov M. G., Kharlamov V. V., Buznik V. M., Ivanov D. M., Pavlushko S. G., Tsvetnikov A. K., Tribological properties of the grease containing polytetrafluorethylene and ultrafine diamond, Friction and Wear, 25 (1), 99 (2004)).
Dispersion of nanoparticles and other AW/EP additives in oils often required dispersants. The ash-less dispersants commonly used in the automotive industry contain a lipophilic hydrocarbon group and a polar functional hydrophilic group. The polar functional group can be of the class of carboxylate, ester, amine, amide, imine, imide, hydroxyl, ether, epoxide, phosphorus, ester carboxyl, anhydride, or nitrile. The lipophilic group can be oligomeric or polymeric in nature, usually from 70 to 200 carbon atoms to ensure oil solubility. Hydrocarbon polymers treated with various reagents to introduce polar functions include products prepared by treating polyolefins such as polyisobutene first with maleic anhydride, or phosphorus sulfide or chloride, or by thermal treatment, and then with reagents such as polyamine, amine, ethylene oxide, etc. Of these ashless dispersants the ones typically used in the petroleum industry include N-substitued polyisobutenyl succinimides and succinates, allkyl methacrylate-vinyl pyrrolidinone copolymers, alkyl methacrylate-dialkylaminoethyl methacrylate copolymers, alkylmethacrylate-polyethylene glycol methacrylate copolymers, polystearamides and other dispersants.
There have been various patents filed on lubricants containing detonation nanodiamonds. (See, e.g., E.P. Pat. 1,980,609, E.P. Pat. 1,953,214 and Rus. Pat. Nos. 2356938, 2054456). However, in order to achieve lubricants with not only low friction coefficient and antiwear properties, but also improved extreme pressure properties, the synergistic mechanisms provided by the addition of a combination of nanodiamonds and various additive components will be described herein.